Muffler



March 14, 1939. G. H HEDRICK MUFFLER Filed Nov. 25, 1938 Patented Mar. 14, 1939 UNITED STATES PATENT OFFICE MUFFLER Application November 25, 1938, Serial No. 242,380

This invention relates to both silencing and exhausting gases flowing from an internal combustion engine. Constructions for this purpose are commonly called "mufliers, and, while principally employed for automotive use, have wide application in connection with internal combustion engines generally and other situations where an explosive exhaust gas must be silenced and dissipated. Mufller constructions now available for the purpose satisfactorily suppress the noises incident to vibrations carried by a pulsating current of gas, but present the objection that the travel of the gas through the muflier is not sufliciently rapid and free as to insure against the building up of an appreciable back pressure. It is recognized by engineers that such back pressures interfere with the efficiency of operation of an internal combustion engine.

:0 The employment of Venturi devices or tapered nozzle means in mufliers some of which include the use of a cooling principle has been proposed, and while" somewhat more efiicient than other types of mufilers, do not overcome the problem of reducing the back pressures to a minimum because they rely upon or permit the gas stream to undergo objectionable expansion during travel through the mufiier. The present invention is an improvement over mulilers of this type and 0 enables the article to be made simply and inexpensively while, at the same time, possessing the desired silencing qualities and freedom from back pressure.

. I have discovered that by providing a mufller in which the exhaust gases are first allowed to expand in the mufller and are then immediately sub-divided and maintained in a plurality of streams, one of relatively high velocity and low pressure and the other of relatively low velocity and high pressure and the pressure at all times is positively held substantially below the pressure of the initially expanded gas, that the gases flow rapidly and smoothly through the muflier whereby the muiller has the desired silencing function and back pressure is rendered negligible.

That is to say, the initially expanded gases are formed into and maintained in a plurality of streams by appropriate means comprising perforate members and associated elongated tapered 0 nozzles or Venturi devices. The nozzles are disposed in alignment and it is critical that their adjacent ends be spaced such a distance as -(1) will prevent any substantial expansion or interference with the positive flow of the high velocity 5 stream, but (2) will allow the low velocity stream to expand and be entrained due to the positive aspirating efiect created by the high velocity stream. The incidental expansion of the high velocity stream as it traverses the enlarged ends of the respective nozzles is found to be negligible in affecting the aforesaid results, and the gases travel through the muflier with a smoothness which permits a higher rate of speed than has heretofore been obtained.

The accompanying drawing illustrates a pre- Ierred embodiment of the invention, and it is to be understood that the mufller may vary as to its details without departing'from the spirit of the invention.

Referring to the drawing, 5

Figure 1 is a longitudinal view partly in sec-- tion;

Figure 2 is a section on the line 2-2 of Figure 1;

Figure 3 is a section on the line 3-3 of Figinc 1; and

Figure 4 is a sectional view of another embodiment of the invention.

Referring to Figure 1, 'the muflier includes the usual preferably cylindrical hollow body I 0 which may be of conventional shape and will be of a length suitable for the particular engine with which it is associated. In this connection, it is an important feature of the present invention that a mufller of substantiallyv less length than those usually required maybe employed by reason of the improvements to be now described.

The body In is closed at its ends by suitable caps H to which are. connected the inlet I! from the engine and the outlet l2 to the atmosphere. These caps may be suitably welded to the inner wall of the body ID by welding as shown at l3.

The muiiler is provided interiorly with a plurality of stream dividing and maintaining means indicated as a whole at 14. As'many of these means may be employed as required, and each of such means includes a perforate member l5 and a tapered nozzle or Venturi device IS. The perforate members l5, while preferably in the form of discs each having a multiplicity of .circularly arranged openings l1 therein as shown in Figure 2, may be in the form of spiders for supporting the tapered nozzles substantially centrally of the hollow body I 0 and in alignment with each other. Each disc l5 has an outwardly turned flange l8 preferably welded to the inner wall of the body and a central opening l9 provided with a flanged wall 20 to which the Venturi device is suitably connected as by welding and supported in the required position. The

Venturi member I6 is preferably, although not necessarily provided with a plurality of. openings 2| formed by striking the metal thereof inwardly to produce a plurality of vanes 22 as shown in Figures 1 and 3. I

Referring to Figure 1, it is-to be observed that the disc l5 adjacent the inlet side of the muiiler is spaced from the cap a distance suflicient to produce an expansion chamber 23 in which the gases discharged from the engine instantaneously and continuously expand. This expansion of gases within the chamber 23 produces a condition of optimum muflier pressure which must be immediately dissipated. The term "optimum pressure is used to describe the condition in the expansion chamber 23. That is, as the gas expands into this chamber, the optimum pressure created is materially lower than that existing in the muffler inlet pipe and the gas flow through the muffler being immediately established, this pressure is not only rapidly dissipated, but is never exceeded throughout the mufiier. In other words, the highest pressure in the mufller is in the expansion chamber, and this, as explained, is appreciably lower than the pressure in the inlet pipe. In accordance with the present invention, I accomplish this result by causing a rapid and positive distribution of the pressure, 1. e., dividing of the gas into separate streams A and B. The stream A will pass through the adjacent tapered nozzle or Venturi device and the other stream B will pass through the openings i1 andinto the passage 24 defined between the outer wall of the nozzle and the wall of the body. It will be noted that the stream A passing through the Venturi member will have a progressively increasing velocity and progressively decreasing pressure, while the stream B surrounding the nozzle will have a progressively increasing pressure and a progressively decreasing velocity by reason of the increase in volume of the flow passage surrounding the nozzle. It is, moreover, to be noted that the path of stream B is circuitous while the path of stream A is direct and uninterrupted. Where the vanes 22 are employed, they do not obstruct to any appreciable extent the velocity of flow through the Venturi nozzle, but in some ases have been found desirable while in other e es are not required.

The forming and maintaining of substantially separate streams A and B continues throughout the muiiier by reason of the presence of a suitable number of the stream forming and maintaining means, and it is to be noted that the streams are substantially concentric and simultaneously flow in the same direction.

The position or proximity of the discs and associated Venturi devices with relation to each other is a critical factor in insuring that the initial pressure created in the expansion chamber 23 will be rapidly and smoothly dissipated. To this end, and regardless of the engine involved, the size of the muflier, the size of the stream forming and maintaining means andthe openings therein, I have discovered that no opportunity must be aflorded for any substantial expansion of the gases of stream A which would result in an objectional increase of pressure and a consequent decrease in. velocity. In other words, this stream should travel continuously and positively at a high velocity and in an uninterrupted path through the muflier from end to end which result is attained by having the nozzles of a length to substantially bridge the space between consecutive perforate members. Furthermore, I have discovered that it is essential that the gases of stream B be allowed to expand into stream A at a plurality of points of low pres sure and be entrained therewith. Therefore, in assembling the mufller, the adjacent ends of the tapered nozzles should be. so positioned as will produce these results. That is, the gases issuing from each Venturi nozzle should pass into the enlarged end of the next nozzle without substantially any of the gas of stream A expanding beyond the venturi and so that the low pressure condition of stream A will cause at least a portion of stream B at these spaced points to expand into stream A and be entrained therewith. This result is attained by causing the gases issuing from the small end of the Venturi nozzle to have such a high velocity that they will carry at least a portion of the gases from stream B with them into the entrance of the succeeding Venturi, i. e., the high velocity stream will have an aspirating effect upon the gases in the surrounding low velocity stream. If the position of the Nenturi members is so controlled, then the dissipation of pressure from the expansion chamber 23 is not only rapid, but of equal importance, smooth to the extent that back pressure becomes negligible and the muflier exerts the desired silencing function. Stated another way, after the creation of an optimum muiller pressure in the chamber 23, it is essential that the gas stream A which traverses a path through the nozzles is always at a high velocity, but at a pressure very substantially below that of the initial optimum expansion pressure.

While the velocity varies slightly as the stream A traverses the tapered Venturi devices, the average velocity is never below that which will produce the most efficient aspirating eiiect.

In another embodiment of the invention shown in Figure 4 the smaller ends 30 of the preceding nozzles extend into the larger ends ii of the succeeding nozzles .to obtain the desired aspirating effect. In this construction also it will be noted that the nozzle membersare of a length to bridge the space between the perforate means.

I am aware that a certain amount of cooling and contraction of the gas takes place during travel through the mufiler, but according to my observation, this result is insufiicient of itself to produce the desired elimination of back pressure and it is necessary that the gas be conveyed at high speed through the mufiier in the manner above described if the desired silencing eflect and reduction of back pressure is to be attained.

As explained above, in addition to eliminating objectionable back pressure, the device of the present invention exerts an improved muilling action. Apparently, the sound energy wave caused by the explosion of the gases will be conducted along the exhaust pipe I2 and issue into the inlet of the muiiier. By analogy to the well known example of a stone cast into a pond to establish a system wave, a spherical wave front is immediately established by the sound energy wave as it issues from pipe I2. A portion of the sound energy will flow outwardly on this spheriical front into the expansion chamber and through the longitudinal path provided both through and about the tapering nozzles.

The sound wave passing into the expansion chamber will be reflected from the walls, against which it impinges, at an angle so that the reflected energy will be more or less out of phase 'wlth the following wave crests, and being out of phase, will tend to neutralize such following crests. The portion of the sound wave entering the nozzle passage will be partially reflected from the tapered wall of the nozzles to establish an out of phase relationship between the reflected crest and the crests flowing straight through, such that the energy of the sound wave is dissipated by the interaction of the reflected wave energy and the energy of the flow passing straight through the nozzles. A similar interaction appears to take place in the path defined between the muffler wall and the outer wall surfaces of the nozzles.

The establishment of this out of phase relationship between various portions of the sound wave is repeated at each of the gas stream forming and maintaining means, i. e. at the nozzle structures, so that before the sound wave has reached the outlet end of the mufller its energy has been completely dissipated by reflection upon itself.

I claim:

1. A mufller including a hollow body, said body having an inlet and an outlet at opposite ends, a plurality of stream forming and maintaining devices fixed in said muffler and each including a perforate member and a tapered nozzle with the nozzles disposed substantially in alignment and said perforate members extending transversely of the muffler body, one of said transverse perforate members forming with the wall of the body an expansion chamber, the perforate members and tapered nozzles dividing the gas introduced to said expansion chamber. into a plurality of streams, one of which travels through said nozzles at a high velocity and has a low pressure and the other of which travels about said nozzles at a low velocity and has a high pressure, each tapered nozzle being of a length to substantially bridge the space between consecutive perforate members and there being openings between the reduced end of one tapered nozzle and the adjacent enlarged end of the succeeding tapered nozzle whereby the high velocity stream flowing through the nozzles will exert an aspirating effect upon the other stream.

2. A mufller including a hollow body, said body having an inlet and an outlet at opposite ends, a plurality of stream forming and maintaining devices fixed in said muiller and each including a perforate member and a tapered nozzle with the nozzles disposed substantially in alignment and said perforate members extending transversely of the muiiler body, one of said transverse perforatemembers forming with the wall of the body an expansion chamber, the perforate members and tapered nozzles dividing the gas introduced to said expansion chamber into a plurality of streams, one of which travels through said nozzles at a high velocity and has a low pressure and the other of which travels about said nozzles at a low velocity and has a high pressure, each tapered nozzle being of a length to substantially bridge the space between consecutive perforate members with the reduced end.- of

' one nozzle extending within the enlarged end of the succeeding nozzle and there being openings between said reduced and enlarged ends of said tapered nozzles whereby the high velocity stream flowing through the nozzles will exert an aspirating effect upon the other stream.

3. A muflier including a hollow body, said body having an inlet and an outlet at opposite ends, a plurality of stream forming and maintaining devices fixed in said mufller and each including a perforate disc member centrally supporting a tapered nozzle with the nozzles disposed substantially in longitudinal alignment and said perforate members extending transversely of the mufller body, one of said transverse perforate members forming with the wall of the body an expansion chamber, the perforate members and tapered nozzles dividing the gas introduced to said expansion chamber into a plurality of streams, one of which travels through said nozzles at a high velocity and has a low pressure and the other of which travels about said nozzles at a low velocity and has a high pressure, each tapered nozzle being of a length to substantially bridge the space between consecutive perforate members and there being openings between the reduced end of one tapered nozzle and the adjacent enlarged end of the succeeding tapered nozzle whereby the high velocity stream flowing through the nozzles will exert an aspirating effect upon the other stream.

4. A muffler including a hollowbody, said body having an inlet and an outlet at opposite ends, a plurality of stream forming and maintaining devices fixed in said mufiler and each including a disc having a circular series of perforations, said disccentrally supporting a tapered-nozzle with the nozzles disposed substantially in longitudinal alignment and said perforate members extending transversely of the mufiler body, one of said transverse perforate members forming with the wall of the body an expansion chamber, the perforate members and tapered nozzles dividing the gas introduced to said expansion chamber into a plurality of streams, one of which travels through said nozzles at a high velocity and has a low pressure and the other of which travels about said nozzles at a low velocity and has a high pressure, each tapered nozzle being of a length to substantially bridge the space between consecutive perforate members and there being openings between the reduced end of one tapered nozzle and the adjacent enlarged end of the succeeding ta- I pered nozzle whereby the high velocity stream flowing through the nozzles will exert an aspirating effect upon the other stream.

5. A mufiler including a hollow body, said body having an inlet and an outlet at opposite ends, a plurality of stream forming and maintaining devices fixed in said muffler and each including a perforate member and a tapered nozzle with the nozzles disposed substantially in alignment and said perforate members extending transversely of the mufller body, each of said nozzles having a plurality of openings in the wall thereof, one of said transverse perforate members forming with the wall of the body an expansion chamber, the perforate members and tapered nozzles dividing the gas introduced to said expansion chamber into a plurality of streams, one of which travels through said nozzles at a high velocity and has a low pressure and the other of which travels about said nozzles at a low velocity and has a high pressure, each tapered nozzle being of a length to substantially bridge the space between consecutive perforate members and there being openings between the reduced end of one tapered nozzle and the adjacent enlarged end of the succeeding tapered nozzle whereby the high velocity stream flowing through the nozzles will exert an aspirating effect upon the other stream.

6. A mufiler including a hollow body, said body having an inlet and an outlet at opposite ends, a plurality of stream forming and maintaining devices fixed in said mufller and each including a perforate member and a tapered nozzle with the nozzles disposed substantially in alignment and said perforate members extending transversely of the mufller body, one of said transverse perforate members forming with the end wall of the body an expansion chamber directly communicating with the inlet, the perforate members and tapered nozzles dividing the gas introduced to said expansion chamber into a plurality of streams, one of which travels through said nozzles at a high velocity and has a low pressure and the other of which travels about said nozzles at GALE HOL'BROOK HEDRICK. 

